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Near-death experiences: products of carbon dioxide, or more complex?

Are near-death experiences all in the head? How about the blood? A recent study has found a link between elevated carbon dioxide levels in cardiac patients’ bloodstreams and eerie experiences such as life reviews, meeting with deceased relatives, and passing through a tunnel of light. The study has led some commentators to suggest that all near-death experiences, or NDEs, are produced by excess carbon dioxide in the blood at the time of resuscitation. So do we now understand all there is to know about NDEs? Not so fast – science is rarely that simple.

Slovenian researcher Zalika Klemenc-Ketis and colleagues at the University of Maribor surveyed 52 cardiac arrest survivors to determine whether they had experienced near-death phenomena during their trip to the hospital and subsequent resuscitation. Respondents were also asked about things like their religious beliefs, educational level, and demographic background. Finally, results of the survey, published in the online journal Critical Care, were correlated with blood samples that hospitals had kept on file for each patient. A statistical analysis revealed that patients whose blood had contained higher-than-average levels of carbon dioxide at the time of their admission to hospital were more likely to have later reported an NDE, an association that was statistically significant. Numerous writers and outside observers have cited Klemenc-Ketis’s results as strong evidence that near-death experiences are purely biophysical phenomena. After all, if something as simple as elevated blood CO2 levels can seemingly cause them, why look for more extravagent explanations like the presence of spiritual beings?

Other researchers, however, claim that the study is less conclusive than it might seem. University of Virginia psychiatrist Bruce Greyson, for example, has pointed out that other studies have found precisely the opposite correlation, showing that patients with lower blood levels of CO2 were more likely to have NDEs. Greyson further claims that Klemenc-Ketis’s study examined too many variables, a common mistake sometimes known as the "pattern-seeking fallacy" – making it likely that at least one of the variables, in this case carbon dioxide levels, would appear to be related to NDEs.

The flurry of interest in the Klemenc-Ketis study, and the fervor with which many researchers defend their interpretations of the data, illustrates one element in the debates on NDEs that has remained the same over the years – some researchers are convinced that NDEs are biological, and others are equally as convinced, it seems, that the experiences in fact represent genuine encounters with a spiritual reality. (Bruce Greyson, for example, is a parapsychologist who has published extensively, and sympatheticaly, on NDEs – one can imagine where his opinion lies.)

While most of us wish science were purely objective, a priori commitments often inform scientists’ interpretation of results and their research methodologies. In the case of NDEs, these ideological tugs-of-war mean that many of the subtleties and subjectively powerful characteristics that make NDEs compelling research subjects can be lost or, at the risk of editorializing, miscategorized. While physiology is undoubtedly related to NDEs, for instance, using physical explanations such as oxygen or carbon dioxide levels in the blood to “explain away” near-death experiences puts researchers at risk of misrepresenting the clinically relevant or religiously textured aspects of the phenomenon, such as the tendency of NDE survivors to report reduced fear of death and a greater capacity to empathize with others after their experience. Would proof of a physiological origin for NDEs that mean that these most compelling aspects of near-death experiences were not, in fact, spiritually meaningful?

Regardless of their provenance, near-death experiences tell us something deeply fascinating about human life and our psychological makeup – even at the final moments of our biological existence, our most passionate concerns appear to be loved ones, our lived narratives, and the very meaning of life and death: a far cry from the terror and agony one might expect. It is at junctures such as these, in which deeply impacting but difficult-to-explain experiences serve as both targets and heroes for people with commitments to particular worldviews, that the true tension between religion and science is brought into sharpest relief.

Readers interested in learning about the sharply contrasting views on NDEs can click here for relevant and compelling excerpts from skeptic Susan Blackmore's book, Dying to Live, and here for the homepage of the International Association for Near-Death Studies.